There is an increasing need for complex three-dimensional (3D) parts having high-performance mechanical and thermal properties. One attempt at meeting this need has been to combine unique properties of different materials to yield 3D parts of functionally gradient properties. Because some materials have desirable properties in some aspects (such as resistance to high temperatures) but less desirable properties in other aspects (such as toughness and/or shock absorption), attempts have been made to combine and grade different materials to make parts for use under critical or extreme service conditions. These attempts have met with limited success.
Several additive manufacturing techniques have been developed or modified to fabricate three-dimensional ceramic components, including 3D Printing, Ink-jet Printing, Selective Laser Sintering (SLS), Stereolithography (SLA), Laminated Object Manufacturing (LOM), and extrusion-based techniques. All of these techniques involve adding materials layer by layer.
Extrusion-based methods are among the most popular approaches due to the simplicity and low cost of their fabrication system, high density of their products, their capability of producing parts with multiple materials and functionally graded materials, and low amount of material wastage during pre-processing and processing. Major extrusion-based processes that have been developed include Extrusion Freeform Fabrication (EFF), Fused Deposition of Ceramics (FDC), Robocasting (RC), and Freeze-form Extrusion Fabrication (FEF).
EFF is the first technique developed to utilize extrusion of ceramic slurries to produce three-dimensional components. In this process, slurries of ceramic powders (such as alumina, silicon nitride, and the like) are prepared in liquid acrylic monomers and other organic-based media, and then deposited onto a (sometimes preheated) platen. This process is also the first extrusion-based process to produce ceramic-based functionally graded materials such as ceramic oxides graded to Inconel or stainless steel.
FDC uses a modified Fused Deposition Modeling (FDM) system to extrude ceramic-loaded thermoplastic filaments. The filament is liquefied, extruded, and re-solidified to retain its shape.
In RC, typically an aqueous suspension is prepared from ceramic materials (e.g. alumina, silica, lead zirconate titanate, hydroxyapatite, silicon carbide, and silicon nitride) and extruded onto a hot plate to dry and maintain its shape. The main advantage of RC over EFF and FDC is using low amount of binder in the feedstock, which facilitates pre-processing and post-processing.
In the FEF process, an aqueous paste is extruded in a freezing environment to solidify the paste after its deposition. Freeze-drying is then used to remove the water content before sintering. This process is also capable of producing complex and functionally graded parts made of different materials such as alumina, zirconium diboride, boron carbide, zirconium carbide, and bio-active glasses.
The above processes each have their own limitations. The binder removal stage for the EFF and FDC processes is difficult and time-consuming, and sometimes causes severe warpage or other defects. Also, it might require multiple cycles with different atmospheres. For the FDC process, the feedstock preparation is also burdensome and requires several steps. The filament must maintain a high dimensional tolerance to ensure consistent flowrates. Although components of multiple materials could be produced, an FDC system is not capable of mixing these materials to fabricate functionally graded parts. RC is not capable of building large solid parts due to its non-uniform drying, which often causes warpage and cracks in the parts. Furthermore, due to inconsistency in extrudate flowrate and inevitable presence of air bubbles in the suspension, the products are not fully dense and their mechanical strength cannot match that produced by the EFF and FDC processes. These challenges add to ice crystal formation and weak layer bonding in FEF, further decreasing the density and mechanical properties. Furthermore, all of the above processes suffer from nozzle clogging resulted from paste agglomerates in the feedstock and freezing or drying inside the nozzle. Thus, there remain needs for an improved method of manufacturing a complex three-dimensional part. The present novel technology addresses this need.